Interpretive Summary: The oak wilt disease, caused by a fungal pathogen, is a significant killer of red oaks in the Midwestern United States. The disease can be transmitted between trees by insects, and one important vector is a sap beetle called Colopterus truncatus. To understand the dynamics of oak wilt transmission, it is crucial to know about the activity patterns and abundance of the beetles. This is very difficult, however, because of the small size and cryptic nature of the beetles. Recently, the pheromone of C. truncatus was identified and synthesized. (A pheromone is a natural blend of chemicals that insects emit to attract mates). Traps baited with the pheromone can detect the insects with far greater sensitivity than other sampling techniques. In the present study, the pheromone was shown to work in both Minnesota and Illinois. Various doses and blends of the three pheromone components were tested, and only one of the components was found to be crucial for good attraction. The highest of the release rates was most attractive, and furthermore, the pheromone was highly synergistic with fermenting whole wheat bread dough. C. truncatus was most active in Minnesota during the months of April and May. This study demonstrated the effectiveness of the pheromone traps for monitoring populations of this sap beetle and defined several parameters for using the pheromone in future practical management of oak wilt. The information will be especially useful to forest managers and plant pathologists. It will allow them to monitor the flight activity of a key oak wilt vector and thus better understand the dynamics of this disease.

Technical Abstract:
The sap beetle, Colopterus truncatus (Coleoptera:Nitidulidae), is one of the primary vectors of the oak wilt pathogen, Ceratocystis fagacearum, in the north central United States. Male beetles emit an aggregation pheromone that attracts both sexes. Field behavioral assays utilizing various release rates and blends of three methyl-branched hydrocarbon components of the aggregation pheromone showed that flight responses of this beetle were similar in Illinois and Minnesota populations. In both locations, both sexes of the beetle responded synergistically to a combination of the pheromone and fermenting whole wheat bread dough. C. truncatus preferred a high-release rate over a low-release rate of the three-component blend. In both locations, the response of C. truncatus to a simplified version of the pheromone consisting of (2E,4E,6E)-3,5-dimethyl-2,4,6-octatriene (1) and (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-decatetraene (3) was not significantly different from the response to the three-component blend, that also contains the most abundant component (2E,4E,6E)-4,6-dimethyl-2,4,6-nonatriene (2). An experiment in Illinois with all possible combinations of the components clearly demonstrated that the decatetraene (3) was the crucial component in the blend. During a weekly survey over two seasons in Minnesota, C. truncatus flew in response to the three-component pheromone between early April and mid-July, with over 98% of the beetles being trapped between April 14 and June 1.